The present invention relates to devices for heating and controlling the temperature of containers, which containers are to be used for containing biological samples, especially for analysis purposes.
It is a well known fact that chemical analysis, and in particular the analysis of biological samples, must be carried out at a predetermined temperature to obtain correct results. In analysing small quantities of substance (such as the analysis of blood or other organic liquids with modern automatic analysis equipment) it is also important to heat not only the samples and reagents but also the small containers into which the samples and reagents are subsequently transferred to carry out the analysis. In this respect, if the samples and reagents are bought to a given temperature while in their storage containers and then transferred for analysis into small containers (such as the so-called rotors used in automatic analysis machines) not at the same temperature, it is apparent that because of the small mass of the samples and reagents (usually hardly more than droplets), they assume the temperature of the container and so give false analysis results.
To ensure that the required temperature is reached and remains constant with time, the containers containing the samples to be analysed are generally stored in storage equipment in the form of temperature-controlled ovens.
The problem common to such heating systems is that measuring the temperature inside the oven does not always give an exact indication of the temperature within the containers because of the inevitable thermal inertia.
In this respect, especially in the case of automatic machine analysis, withdrawing the containers from the oven only a short time after their insertion may mean that they have undergone insufficient heating. However if they are kept in for a time longer than that strictly necessary to obtain correct heating, and thus with a reasonable chance that the containers (which enter the oven not always at constant temperature) have reached the required temperature, there is a considerable slow-down in analysis rate. In addition, if conventional metods are used to measure the temperature of the interior of the oven and this is kept constant, thermal inertia again means that there can be no guarantee that the container temperature is maintained at constant value, and the containers can therefore leave the oven at the wrong temperature. The aforesaid problems could theoretically be solved by placing a temperature sensor in contact with the containers to obtain direct measurement of their temperature within the oven rather than the temperature of the oven interior itself. This method is however impracticable because any temperature sensor in contact with the containers would also be influenced by the oven internal tenperature which, as stated, is not always in constant relationship with the container temperature.